Conventional vertical semiconductor devices such as trench-gate IGBTs and PIN diodes have a vertical-structure area. Examples of the vertical-structure area include, for an IGBT, an area including in an n-type drift layer an n-type buffer layer and a p-type collector layer, and for a diode, an area including in an n-type drift layer an n-type buffer layer and an n+ cathode layer. The IGBT having the vertical-structure area is disclosed by, for example, Patent Document 1.
Furthermore, the conventional vertical semiconductor devices having the vertical-structure area, such as IGBTs and diodes, adopt wafers manufactured by epitaxial growth as Si wafers from which the semiconductor devices are manufactured.
In the vertical-structure area of the wafer of, for example, an IGBT, an n-type buffer layer has as an impurity profile a profile of impurities with a steep slope and high concentration across a junction between the n-type buffer layer and the n-type drift layer.